BEIJING , China -LRB- CNN -RRB- -- The world will soon see an `` explosion '' of swine flu cases as the H1N1 virus spreads rapidly around the world , a top World Health Organization official said Friday .

Spread of the H1N1 virus is entering an `` acceleration period , '' WHO official says .

Spread of the virus is entering an `` acceleration period '' and it is certain that there will be more cases and more deaths , said Dr. Shin Young-soo , the organization 's regional director for the Western Pacific .

`` Most countries may see a doubling of cases every three to four days for two months until peak transmission is reached , '' he said at a symposium in Beijing , China . `` At a certain point , there will seem to be an explosion in case numbers . I believe it is very likely that all countries will see community-level transmission by the end of the year . ''

More than 1,490 people around the world have died from the virus since it emerged this spring , Shin said .

Swine flu is the first influenza pandemic in more than 40 years . So far , it has caused mostly mild illness , but Shin warned `` the virus has a sting in its tail '' because it is very infectious and `` has the potential to cause more serious disease . ''

Any widespread resistance to antiviral drugs , expected to be available this fall , could make the situation worse , he said .

The virus so far has shown itself to be unpredictable , Shin said , so the public needs to be prepared . He called for accurate and timely public health messages and early treatment of severe cases .

The public needs to comply with these health messages , and everyone needs to be able to recognize symptoms early and get timely medical care , he said .

`` We will only be safe when we have applied these lessons in every country dealing with this virus , '' Shin said . `` We need to learn quickly since , as I believe , it appears that this pandemic will get worse before the situation gets better . ''

@highlight

Spread of the virus is entering an `` acceleration period , '' official says

@highlight

Countries may see a doubling of cases every three to four days , he says

@highlight

More than 1,490 people have died from the virus since last spring

@highlight

H1N1 is the first influenza pandemic in more than 40 years